However once Fulgrim arrived, he transformed the planet. Terraforming technology was reinvented, allowing forests, oceans, plains and rainforests to spread from the reclaimed outposts and bring life to the planet. As beautiful forests were planted on ground once mined for metals, the skies became blue again and wondrous cities of glass, gold, crystal and steel rose to new heights of glory, Fulgrim's presence drove a resurgence of craft, art and intellectual refinement.
After the Horus Heresy, all life on Chemos was destroyed by Imperial forces and its location is unknown. It may have been located in the area of the Khymaran Drift, close to the Maelstrom, but it is impossible to be certain.
Where is Chemos located in real life astronomy?
In real life astronomy, scientists also divide up the galaxy into four quadrants. The fourth galactic quadrant corresponds partially with the Segmentum Ultima. The 4th galactic quadrant is mostly only visible from the southern hemisphere.
Real life astronomy indicates that the constellation of Sagittarius is located at approximately 0 degrees. The constellation of Vela (Argo) is located at about 270 degrees.
Chemos is located closer to the galactic core than 270 degrees, so presumably it should be closer to Sagittarius than Vela. At approximately the right spot between the two is the constellation of Pavo, the peacock. Moreover the closest star in Pavo is 12.57K light years away from Terra, meaning that another star in the constellation could potentially be 17.5K away. So we can pretend that Chemos is located where Pavo sits in the Terran night sky.
There are of course a number of major flaws with my methodology. First of all, stars are constantly moving. The constellations in the year 2K are certain to be different in the year 30K. Secondly, constellations are a matter of perspective from the vantage point of Terra. A constellation can be made up of a number of stars which are in reality quite far from one another in distance. Third, eyeballing the distances can hardly pretend to be an exact science, and is highly inaccurate.
Nevertheless, it is an interesting fantasy to imagine that Chemos could have been located in a constellation of a peacock.